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Blood Thinner Doesn't Prevent Miscarriages: Study

By Brenda Goodman, MA
WebMD Health News

Reviewed by Brunilda Nazario, MD

July 25, 2014 -- Injected blood thinners don't prevent pregnancy complications in women who may be prone to blood clots, a new study shows.

Women who have had miscarriages are often given blood tests to check for genetic problems that may lead to blood clots.

These inherited clotting problems affect about 1 in 10 people in North America, according to study researcher Marc Rodger, MD. He is a senior scientist at the Ottawa Hospital Research Institute in Canada.

The fear is that having one of these clotting problems may cause clots to form in the placenta, choking the delivery of oxygen and nutrients to a growing baby.

Research in the past suggested that having a clotting disorder might be tied to miscarriage, so about 15 years ago doctors began to prescribe the blood thinner heparin, which is sold under the brand names Fragmin, Innohep, and Lovenox, to help prevent them and other serious problems like preeclampsia.

"And that led to a lot of docs prescribing this medication and a lot of patients demanding this medication, because there's really very little that can be offered to [these] patients," Rodger says.

But these blood thinners may not work as well as doctors had hoped.

Blood Thinners Not Needed?

In the new study, which is published in TheLancet, doctors recruited 292 pregnant women who had clotting disorders confirmed by blood tests. They were also considered to be at high risk for pregnancy complications because they had a history of preeclampsia, pregnancy loss, blood clots in a leg or lung, a low-birth-weight baby, or a placental abruption, where the placenta separates from the wall of the uterus before delivery.

Researchers randomly assigned about half the women to get daily injections of the blood thinner Fragmin. The other half didn't get the injections. Most started the injections around the 12th week of pregnancy and continued until week 37.

About 1 in 6 women in the study had a serious pregnancy complication during the study. Those included blood clots, high blood pressure and mild kidney failure, birth of a baby that was small for its age, or a miscarriage.

But there was no difference in the number of those complications between the two groups.

"We basically showed a daily injection of blood thinner throughout pregnancy is ineffective at preventing pregnancy complications," Rodger says.

But women who took the blood thinner did have more minor bleeding, like nosebleeds, gum bleeds, and vaginal bleeds. They were also more likely to have allergic reactions to the medication.

And they had to suffer through the pain of daily injections in the stomach or thigh.

During the average pregnancy, a woman will need about 400 such injections at a cost of about $8,000 before insurance, Rodger says.

Blood Thinners 'Overprescribed'

"It is discouraging, but on the other hand, it saves a lot of women the burden of giving themselves injections, and now doctors can have evidence-based discussions instead of hope-based discussions with patients," he says.

Other experts who were not involved in the research agree.

"I would like to think that it will change practice," says Catherine Herway, MD, assistant director of obstetrics and maternal/fetal medicine at Staten Island University Hospital in Staten Island, N.Y.

Blood thinners, she says, are "way overprescribed in pregnancy."

She says she sees many patients who are referred to her because tests show they have blood clotting genes but may not have a history of clots.

Those patients sometimes demand to be given heparin. "For some reason, they think it's going to be the miracle drug that's going to save their baby," she says.

She says she hopes the study will help patients and doctors be more thoughtful about taking blood thinners.

Rodger says the study's results don't apply to all women. He says that in women who've had a history of deep vein thrombosis -- blood clots in deep veins in the body -- and those with certain autoimmune diseases, there is some evidence that taking blood thinners during pregnancy can help. But he says those are relatively rare cases, and that most women, even if they've had several miscarriages, probably won't benefit from the drugs.

Herway agrees: "It's hard to tell patients no sometimes, but sometimes it's in the patient's best interest to do what science tells us to do."

SOURCES: Marc Rodger, MD, senior scientist, Ottawa Hospital Research Institute, Canada, Catherine Herway, MD, assistant director, obstetrics and maternal fetal medicine, Staten Island University Hospital, Staten Island, N.Y. The Lancet, July 24, 2014.

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